Plot: Like a serene swan paddling madly under the surface, it takes a lot of hidden choreography to keep a luxury hotel afloat. Food critic Giles Coren and chef Monica Galetti go behind the scenes of the world’s most impressive hotels - from Singapore’s Marina Bay Sands, with rooftop gardens longer than the Eiffel Tower is tall, and Nairobi’s Giraffe Manor, where standards are as high as necks are long